SBN (strontium barium niobate) is a ferroelectric inorganic crystal belonging to tungsten bronze type, and has the Curie point thereof at near room temperature. As for the application to electrical materials, the SBN is being put to practical use as a surface acoustic wave material, since it has piezoelectric property and pyroelectricity because of the ferroelectric property thereof, and especially the piezoelectric property is significant. Further, since a SBN single crystal transmits light, it is expected to be applied to an opto-electronics material for advanced information communication and processing. It is expected that SBN is used in broad range of applications.
Though the SBN has a fine characteristics as described above, only SBN single crystal has been supplied. Since the single crystal has no pores leading to scattering of light and phonon, it has high performances in dielectricity and opto-electronics. However, manufacturing the single crystal requires advanced techniques, it is difficult to produce it in large quantities, and it is inevitable to be high priced.
In order to cope with these problems, a SBN ceramic was developed. S. B. Deshpande et al. measured various electrical properties of SBN ceramics, and obtained the ceramic having the Sr/Ba ratio thereof of 0.50 and dielectric constant ε1 of 1100 (30° C.) (J. Amer. Ceram. Soc., 75[9]2581–85 (1992)). However, pores in the sintered body of a ceramic cause dispersion of light and phonon and decrease of its mechanical strength and electrical properties.
Recently, a glass ceramics has been known as a material which overcomes the defects of ceramics. The glass ceramics is fabricated by crystallizing the glass. It is aimed that mechanical properties, electromagnetic properties, optical properties and thermal properties can be controlled by the size and the amount of the deposited crystal and the combination of the deposited crystal and glass matrix. However, techniques have not been accumulated to rise to the level where the properties are freely controlled.
In 1964, A. Herezog disclosed a research of barium titanate glass ceramics as a trial to obtain a glass ceramics applicable to a ferroelectric application. The disclosed glass ceramics consists of dielectric crystals of 1μ or less in average and glass matrix. Further, it does not contain micro pores, dose not allow gas and liquid to pass through, and has large dielectric constant despite it contains much matrix.
Furthermore, in December 2000, Jiin-Jyh Shyu, et al. presented a paper disclosing SBN glass ceramics produced by crystallizing a glass of 22.5SrO-22.5BaO-20Nb2O5-35SiO2 (mol %). It was disclosed that the glass ceramics shows the dielectric constant thereof of 190 (1 kHz) (J. Amer. Ceram. Soc., 83[12]3135–40(2000)).
The object of the present invention is to provide an economical SBN (strontium barium niobate) glass ceramics having superior dielectric constant and transparency.